photons has no mass ,in relativity any thing that moves in the speed of light has the mass of infinite ,then photons have to be with the mass of infinite, so why does photons are being an exceptional case ?
Photon doesn't have any rest mass. According to Einstein, anything which have rest mass would have infinite mass at speed of light. m' = mγ. As velocity tends to c, the factor γ tends to infinity. Thus m would be infinite. But for photons, at speed of light, m = 0/0 (actually meaningless!!). But would mean it is a finite mass.